The present invention relates to apparatus for optical scanning of light-transmitting flexible sheet-like carriers of information, especially microfilms or twin-layer test films whose gradation is different for different colors of copying light. More particularly, the invention relates to apparatus wherein a sheetlike carrier of information is moved in several directions by one or more power-driven components so as to place selected portions of the carrier in register with a reference point, e.g., with a source of light and a photoelectric transducer or a magnifying lens system. The selected portions of the carrier can be viewed on a screen, or the information which is obtained as a result of scanning can be transmitted to the evaluating circuit of a computer or the like.
Certain presently known reading apparatus for microfilms or the like are provided with means for moving a sheet-like information carrier in several directions with respect to an optical scanning unit. In a microfilm reader, the light source emits a bundle of light rays which suffices to illuminate an entire film frame, e.g., a miniature image of an entire page in a book, publication or the like. The image of the frame is enlarged by a suitable optical system which projects the enlarged image onto a screen.
Similar apparatus are used in the field of graphic arts to scan test images of wedge-like grey filters which are exposed onto sheets of photographic film. The scanning is utilized to determine proper exposure conditions. Still further, similar apparatus can be used for effecting exposure of photographic films which are to be used for storage of microimages or in the graphic arts.
German OS No. 2,313,349 discloses an apparatus which can control the exposure of photographic films to light. In the first step, one produces a test film by copying a wedge-like filter with light in two colors whereby the ratio of the two colors varies at right angles to the direction of change of filter density. The two colors effect different gradation of the material. Based on its maximum and minimum densities, the film can be used to calculate the combined exposure time in the two colors and the ratio of the colors. The test film renders it possible to avoid a series of calibrating operations because it is treated in the same way as the actual copies, i.e., the density values of the test film can be compared with desired density values of the copies to obtain the optimum values for exposure of copies to photographic light. The exposure of test film preferably takes place in the apparatus which is used for the making of copies. This insures that no exposure errors can occur as a result of differences between the characteristics of two or more discrete copying apparatus.
German Pat. application Ser. No. P 25 12 055. discloses an apparatus wherein a test film or an analogous carrier of information is mounted in a circumferentially complete frame prior to scanning by means of a device including a light source and a photosensitive transducer. The mounting of carriers in a frame takes up substantial amounts of time. Furthermore, the frame is sturdy and its mass is considerable so that the apparatus must be equipped with powerful prime mover means and bulky motion transmitting means for shifting the frame and the carrier therein relative to the scanning system. Alternatively, the scanning system must be moved relative to the frame.